The present invention relates to a cooling system for a variable vacuum capacitor.
In the prior art, for various purposes, fixed vacuum capacitors with a certain capacitance and variable vacuum capacitors with a capacitance that is adjustable within a certain range are used. Vacuum capacitors may be used in broadcast systems, in systems for the production of flat panel displays or semiconductors, or in other industrial applications. Vacuum as a dielectric medium offers many advantages. Because of the high dielectric strength, it is possible to maintain very close plate spacing and still have a capacitor with good high voltage capabilities. Should a breakdown occur in a vacuum capacitor, this does not normally result in permanent damage which is often the case with capacitors with other dielectrics, such as paper, SF6, or other dielectrics. Variable vacuum capacitors often comprise a first electrode that, by means of a metal bellows, is movably arranged with respect to a first part of the housing of the variable vacuum capacitor. An insulator is tightly connected between the first part of the housing and the second part of the housing. The second part of the housing comprises a second electrode. A vacuum that extends between the first electrode and the second electrode is established inside the housing. With such an arrangement, a variable capacitor is established, wherein the capacitance of the variable capacitor depends on the distance between the first, movably arranged electrode and the second electrode. When such a variable vacuum capacitor is in use, electrical energy is transmitted over the metal bellows between the first part of the housing and the first electrode. The metal bellows has to be flexible enough to allow a smooth movement of the first electrode and, as well, the metal bellows has to be a good electrical conductor. However, these requirements are difficult to achieve at the same time. Therefore, when such a variable vacuum capacitor is used in high energy applications, excessive heat energy may be produced in the metal bellows. In prior art, water cooling systems have been used to provide a sufficient cooling of a variable vacuum capacitor. In the document CH656740, a turbulence water cooling system with a high efficiency is described. Water cooling systems are arranged such that a water stream is guided inside the metal bellows, thus enabling an efficient cooling of the metal bellows. A drawback of a water cooling system is that distilled or de-ionized water has to be used. Moreover, the water purity and flow protection should be periodically checked to insure against excessive degradation. Water purity can be seriously degraded by contaminants from the various cooling system components. For example, free oxygen and carbon dioxide in the coolant will form copper oxide on the surfaces, thereby reducing the cooling efficiency. Moreover, if a water cooled vacuum capacitor is not used for a certain time period, a complicated drying procedure has to be applied first, in order to avoid corrosion.
It is desirable to propose a new cooling system for a variable vacuum capacitor, which cooling system does not have the drawbacks of the prior art. In particular the new cooling system shall allow usage of conventional industrial water, and the risk of corrosion when the variable vacuum capacitor is not used for a certain time period shall be reduced.
In an aspect of the present invention a liquid is arranged inside a closed cooling reservoir, that a first part of the reservoir is designed to absorb heat energy from first bellows of the variable vacuum capacitor, said first bellows being responsible for transporting electrical energy to a first electrode of the variable vacuum capacitor, that a second part of the reservoir is designed to dissipate heat energy towards a cooling circuit, and that heat pipes are arranged between the first part of the reservoir and the second part of the reservoir. In particular, the cooling circuit can be easily designed in such a manner that conventional industrial water without any purification can be used. Moreover, the risk of corrosion in the cooling circuit is drastically reduced. For example, the cooling circuit can be manufactured in stainless steel material. Moreover, the drying procedure of the cooling circuit is simplified. For example, a simple drying by means of high pressure air may suffice.
In an embodiment variant, the liquid arranged inside the closed reservoir comprises oil. In particular, such an embodiment variant has the advantage that a relatively cheap liquid with appropriate thermal and electrical properties may be arranged in the cooling reservoir.
In another embodiment variant, the cooling circuit is manufactured in stainless steel material or in any other material resistive to corrosion and capable of transmitting heat energy at the same time. In particular, such an embodiment variant has the advantage that conventional industrial water may be used for heat energy transportation in the cooling circuit.
In another embodiment variant, the cooling circuit comprises means for dissipating heat energy to a surrounding. Such means may comprise any type of heat exchanging device. For example, a heat exchanging device may comprise several laminations for dissipating heat from a metal body to the air.
In another embodiment variant, orifices are arranged between the first part of the reservoir and the second part of the reservoir for enabling a free circulation of the liquid in the reservoir. For good heat energy absorption, the first part of the cooling reservoir has to be arranged close to the location where heat energy is generated. For good heat energy dissipation, the second part of the cooling reservoir has to be arranged close to a location where heat energy can easily be dissipated. Various constructional requirements have to be met when arranging the first part of the reservoir and the second part of the reservoir. It is an advantage, in particular, when orifices are arranged between the first and the second part of the reservoir; a free circulation of the liquid inside the reservoir can be established.
In another embodiment variant, second bellows are arranged for establishing a constant volume of the reservoir. It is an advantage, in particular, that, by means of the second bellows, a closed reservoir that can be fully filled with the liquid can be established.
In a further embodiment variant, the first bellows comprise metal material, in particular bronze or other alloys. It is an advantage, in particular, that materials with well known properties, especially concerning transmission of electrical energy, can be used.
In another embodiment variant, the second bellows comprise plastic material, in particular rubber or other flexible material. It is an advantage, in particular, that materials with well known properties, especially concerning mechanical flexibility, can be used.